Bicycle rims have been in use for over 100 years. Heretofore, most bicycle rims have been made from steel or aluminum. In the past 15 years or so, many bicycle rim manufacturers have begun to make some of their rims out of carbon fiber composites. Carbon fiber composite rims and wheels are especially attractive to those engaged in racing and other pursuits where the lightweight rims are desired.
Many carbon fiber bicycle rims and wheels exist. Many of these rims and wheels can be seen in the COMPOSITECH, INC. catalog of its the ZIPP SPEED WEAPONRY products. Other carbon fiber rims include one manufactured by Specialized Wheel. The Specialized rim has a solid interior construction. Another prior known rim is the Hed rim, which is disclosed in Hed and Haug U.S. Pat. No. 5,061,013. The Hed and Haug patent discloses a wheel having toroidal side surfaces. Preferably, the wheel, when mated to a tire, has an elliptical cross section. An improvement on the wheel shown in the Hed and Haug patent is the HED CX Wheel.
Another carbon fiber rim is shown in Hopkins U.S. Pat. No. 4,919,490.
When designing a bicycle rim, it is important to take into account the stresses and loads that are imposed on the rim that are caused by the varying road conditions to which the rim will be exposed. These stresses include the vibrational and jarring stresses caused by pot holes and road imperfections, and thermal stresses caused by heat induced due to braking.
The problems induced by vibration have been dealt with in the past largely in terms of employing devices for reducing the vibrations to the cyclist. To accomplish this, many bicycles have employed frame suspensions that were designed to attempt to insulate the rider from road vibrations and impacts. One example of such a framed-suspension design is the ZIPP articulated beam containing carbon bodied bicycle frame, which is shown in many ZIPP catalogs.
Unfortunately, very little engineering effort has been devoted to reducing the impact of vibrational forces upon rims. Very little, if anything, has been done, prior to the present invention, to increase the durability of bicycle rims, through choice of material, shape of the rim, or the use of other designed criteria. Further, no known rim designs have been employed, that permit the rim to be used as a means of absorbing impact energy and vibration. To the contrary, the primary means (and usually the only means) within a bicycle tire and rim combination that has been employed for absorbing impact energy and vibration has been the tire attached to the rim.
The sport of mountain biking, and its increased popularity, has created a need for rims to become more durable and better capable of absorbing impacts. This greater need occurs because of the increased vibration and the jarring impact type forces that are imposed on rims of bicycles ridden over rough mountain terrain.
Additionally, the sport of mountain biking tends to impose relatively greater thermal loading stresses upon the bicycle rim. This increased thermal loading is caused by the heat that is built up between the braking surface of the rim, and the inner, flexible side walls of the rim. The problems caused by thermal build-up can be especially troublesome when a two-piece bicycle rim body is used, wherein the two pieces are made from dissimilar materials, such as metal and carbon fiber, having unmatched co-efficients of thermal expansion.
One object of the present invention is to provide a bicycle rim having a design well suited to absorb a vibrational and jarring stress loads. Another object of the present invention is to provide a rim that is capable of withstanding large amounts of thermal loading caused by brake heat build-up.